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Date: 30-07-13

Researchers try out terahertz electrical switch using magnetite material

Today's widely used and popular nanoscale switch, the silicon MOSFET transistor, what we find in Ultra integrated VLSI chips can switch at speeds of 10s gigahertz, speed can be pushed further by using high electron mobility compound semiconductor material. But the researchers U.S. Department of Energy's (DOE) SLAC National Accelerator Laboratory go for a big jump in switching speeds by able to use magnetic material called magnetite as an electric switch at the frequencies in terahertz range, thousand times higher than today's switching in any of the semiconductor material.

Scientists have used SLAC's Linac Coherent Light Source (LCLS) X-ray laser to switch from on to off in 1 trillionth of a second in samples of magnetite.

"This breakthrough research reveals for the first time the 'speed limit' for electrical switching in this material," said Roopali Kukreja, a materials science researcher at SLAC and Stanford University who is a lead author of the study.

Scientists could able to see how the electronic structure of magnetite sample rearranged into conducting and nonconducting regions, which formed in just hundreds of quadrillionths of second. They could see how a conducting and nonconducting states coexist in the material to create electrical pathways in high-speed chips which can be used to process high definition video thousand times faster than the present VLSI chips.

If this research becomes successful it paves way to a new generation of chips which can be configured using light or any such emission.

The process used is somewhat similar to present chipmaking, the laser light was flashed on the sample material resulting in fragmentation of material's electronic structure at an atomic scale. After beaming laser, scientist hit the material with ultrabright, ultrashort X-ray pulse to study the timing and details of changes in the sample excited by the initial laser strike. It's not clear whether they used masks for the material to undergo electronic structural change.

By slightly adjusting the interval of the X-ray pulses, they precisely measured how long it took the material to shift from a non-conducting to an electrically conducting state, and observed the structural changes during this switch, as said in the release.

The release states "Scientists had worked for decades to resolve this electrical structure at the atomic level, and just last year another research team had identified its building blocks as "trimerons" – formed by three iron atoms that lock in the charges. That finding provided key insights in interpreting results from the LCLS experiment."

The magnetite had to be cooled to minus 190 degrees Celsius to lock its electrical charges in place, so the next step is to study more complex materials and room-temperature applications, Kukreja said.

Future experiments will aim to identify exotic compounds and test new techniques to induce the switching and tap into other properties that are superior to modern-day silicon transistors. The researchers have already conducted follow-up studies focusing on a hybrid material that exhibits similar ultrafast switching properties at near room temperature, which makes it a better candidate for commercial use than magnetite, explained in the release.

Hermann Dürr, the principal investigator of the LCLS experiment and senior staff scientist for the Stanford Institute for Materials and Energy Sciences (SIMES), said there is a major global effort underway to go beyond modern semiconductor transistors using new materials to satisfy demands for smaller and faster computers, and LCLS has the unique ability to home in on processes that occur at the scale of atoms in trillionths and quadrillionths of a second.

This research tells, for faster switching it's not just semiconductor material, but also any other materials can be explored for terahertz switches, which are necessary for future computing comparable to human brain.

The institutes collaborating on this project includes Helmholtz-Zentrum Berlin for Materials and Energy; Hamburg University/Center for Free Electron Laser Science (CFEL); University of Amsterdam; the T-REX laboratory at the ELETTRA-Sincrotrone Trieste and University of Trieste; Cologne, Potsdam Regensburg and Purdue universities; the Advanced Light Source at Lawrence Berkeley National Laboratory; and SwissFEL.

Research at Stanford University was supported through SIMES and LCLS by the DOE Office of Science. Portions of this research were carried out on the Soft X-ray (SXR) instrument at the LCLS, a user facility operated by Stanford University for the DOE. SXR is funded by a consortium including LCLS, Stanford, Berkeley Lab, CFEL, University of Hamburg and several other research organizations in Europe.

terhertz switch

An optical laser pulse (red streak from upper right) shatters the ordered electronic structure (blue) in an insulating sample of magnetite, switching the material to electrically conducting (red) in one trillionth of a second. (Greg Stewart/SLAC)

magnetite switch

In its insulating state, the magnetite sample has electrical charges locked into structures known as "trimerons" that are composed of three iron atoms (a). An optical laser pulse was used to fracture trimerons (b), creating strands of electrical conductivity (red) surrounding islands of non-conducting trimeron structures (c). (S. de Jong et al./Nature Materials)

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